Cranes of the larger sizes are typically too large to ship from the facility at which they are fabricated to their installation destination in one piece. They consequently are shipped in a number of disassembled separate pieces and components and assembled at their destination. In particular, gantry cranes of the portal type in which the loads lifted by the crane are moved between the legs of the crane are of a very large size and require a design which enables shipping of load bearing sections in several pieces and assembly of the load bearing sections at the operating location. The manner of assembly of the different sections together to form the finished crane must, of course, not decrease the ability of the crane to handle the large loads and duty cycle for which it is designed.
Portal cranes having overhead truss frames may have frame spans of 250 to 300 feet or more and stand on legs more than 100 feet above the ground. In view of such sizes, the legs of the crane are frequently shipped in two or three sections and the overhead frame may be shipped in three or more sections.
In assembling the various sections of the crane at the installation site, several different types of assembly or joining approaches are used. One well known assembly approach is to provide leg sections or frame sections to be joined with mating flanges which are abutted against each other and bolted together. However, such joining structures, when subjected to the alternating compression and tension stresses produced during the operation of a crane, tend to loosen and therefore require continuous maintenance. This is particularly true of such flange type joints when used in the overhead frame of a portal crane which is subject to both tension and compression as the load which it is lifting and transporting moves along the frame length. Another approach to joining the crane sections together, which produces a high-strength reliable joint, is welding of the sections together. The welded joints, however, have to be non-destructively analyzed to determine their integrity. Although a welded joint meets the reliability and strength requirements of the crane, the welding and the analysis of the welded joint are relatively costly and undesirable for that reason. A third structure used for joining crane sections together is a shear bolt joint in which a pair of facing plates, bridging the two pieces to be joined are bolted through the pieces to be joined and to each other. Although this joining approach is relatively reliable, it is extremely expensive in that a very large number of bolts is required and the labor in assembling the entire joint is substantial.
The applicant's invention is an improvement over the types of joints currently used in joining together crane sections at the site at which the crane is to be operated.